A common type of hearing protector comprises two earmuffs and a headband connecting the earmuffs to one another.
A conventional earmuff usually comprises a cup-shaped cap, an annular bottom plate, a padded sealing ring which is connected to the bottom plate and arranged to abut against a user's head, and stuffing which can be made of foam plastic and is positioned in the cap. The cup-shaped cap and the annular bottom plate are tightly fixed to each other by a conventional snap lock. A conventional snap lock is provided, for instance, by the cap being provided with a projection extending along the opening portion of the cap. The projection is formed on the inside of the opening portion of the cap. The bottom plate has a connecting portion which is arranged to extend a certain distance into the opening portion of the cap. The connecting portion has on the outside a circumferential groove. The groove cooperates with the projection to tightly hold the cap and the bottom plate together.
However, it has been found that two earmuffs which have been manufactured in the same way according to the description above have a tendency to exhibit different damping properties for sound in different frequency ranges. Differences in damping mean that a first earmuff damps sound within a certain frequency range quite well while at the same time a second earmuff damps sound within the same frequency range relatively poorly.
This means in turn that there is a risk that the two earmuffs in one and the same hearing protector exhibit different sound damping capacities, which means that a user catches a certain sound in one way by one ear and in another way by the other ear. This is a drawback since a user has difficulty in determining the direction of sound, which may cause danger on a shop floor.
Owing to the difference, it is also difficult to adjust an earmuff to a specific purpose. To adjust an earmuff to a specific purpose means, for instance, satisfying a requirement that the capacity of damping sound in a certain frequency range be improved. The problem is, among other things, that different earmuffs of the same type damp, as mentioned above, sound in a certain frequency range to different degrees. An adjustment of an earmuff so that it has a good capacity of damping sound in a first frequency range means, in practice, that it is necessary to accept an inferior damping capacity in a second frequency range. The difference in the damping capacity of different earmuffs of the type described above can very well be in the same order as the distance between said first and second frequency ranges.